1. Field of the Invention
Apparatuses and methods consistent with aspects of the present invention relate to a medium feeding unit for loading and supplying a print medium and an image forming apparatus having the same, and more particularly, to a medium feeding unit having an improved structure for sensing the number of loaded print media and an image forming apparatus having the same.
2. Description of the Related Art
An image forming apparatus includes a medium feeding unit provided with a loading plate where a print medium is loaded, and an image forming unit to form a visual image with a developer on the print medium. During a printing operation, the print media on the loading plate are picked up sheet-by-sheet and fed to the image forming unit.
Before the printing operation, the loading plate has to be loaded with the print media. To sense whether or not the print media are loaded onto the loading plate, a sensing unit is installed in the medium feeding unit. With regard to such a sensing unit, various configurations and operating methods have been proposed.
For example, a conventional sensing unit includes a sensor in which a light emitting portion and a light receiving portion are integrated with each other, and a through hole formed in the loading plate that can pass a beam emitted from the light emitting portion of the sensor therethrough. If the loading plate is not loaded with any print media, the beam emitted from the light emitting portion travels undisturbed via the through hole, so that the light receiving portion does not receive any portion of the beam. On the other hand, the through hole is blocked when the print medium is loaded into the loading plate. Therefore, if the loading plate is loaded with some print media, the print media block the through hole and the beam is reflected or scattered from the surface of the print medium so that the light receiving portion can receive a portion or all of the beam reflected or scattered from the surface of the print media. Accordingly, it is possible to sense whether or not print media are loaded onto the loading plate.
However, the conventional sensing unit only senses the existence of print media, so that a user can only recognize absence of print media when the loading plate is empty. In other words, a user does not know whether or not the number of loaded print media is enough to complete the printing operation. Accordingly, when the print media are exhausted the image forming apparatus may suspend printing during the printing operation.
Meanwhile, in the case of a tandem-type image forming apparatus, an image is first formed on an image carrying body or on an intermediate transfer belt before being transferred to a print medium, to thereby enhance speed of the printing operation. However, if the print media are exhausted during the printing operation and the tandem-type image forming apparatus suspends operation, the image previously formed on the image carrying body or the intermediate transfer belt not only is not used but may need to be cleaned off before the image forming apparatus can be used again. Accordingly, problems arise, for example, developer is wasted; the system load increases because of the cleaning process; and the next print medium may be contaminated in the next printing operation.